Journal of
Science and Technology-The University of Danang, JST-UD, is an
independent peer-reviewed journal, applying international standards, inheriting
the achievements of 40 years of scientific and technological information
activities of Da Nang University and member institutions.
JST-UD operates under License No. 510/GP-BVHTT, dated November 25, 2002
by the Ministry of Culture and Information and international standard code ISSN
1859-1531 (according to Official Letter No. 44/TTKHCN-ISSN, February 6, 2007 of
the National Center for Scientific and Technological Information under the
Ministry of Science and Technology). It is a scientific journal with a high
number of access and reference.
JST-UD publishes quality scientific works in Vietnamese, English or
French (License No. 210/CBC, 5 March 2008 of the Press Department, Ministry of
Information and Communication) and Published yearly 15 numbers, including 3 in
English (License No. 07 / GP-BTTTT, January 7, 2016 by the Ministry of
Information and Communication).
The Journal
"Science and Technology" of the University of Danang is for purposes:
- Publishing new and multi-disciplinary
scientific and technological research works;
- Reviewing information on advances in
science and technology for the teaching, research and study of lecturers and
students;
- Propagating the guidelines and policies
of the Party and the State in the fields of education, training as well as in
scientific and technological researches.
JST-UD is pleased to receive many-sided cooperations of scientists,
educators, researchers in and outside the University of Danang as well as
national and international researchers to improve the prestige and the quality
of the Journal.
CURRENT ISSUE | Vol. 18, No. 7, 2020
Author: , Kim Ánh Nguyễn*,
Code: JST-UD2020-001 | Page: 1-6 of Vol. 18, No. 7, 2020 |
Abstract- The quasi-Z-source inverter (qZSI) is recognized as an attractive solution for the photovoltaic system compared with the conventional voltage source inverter due to its benefits such as the capability to boot the DC voltage input and overcome the drawback of the short-circuit effect in switching devices. This paper presents a model predictive control strategy for a grid-connected photovoltaic system using qZSI that achieves fast dynamic response without cascaded control loop structure and modulation block. A mathematical model of the qZSI is used to predict the behavior of the load current, inductor current, and capacitor voltage. A cost function is defined that includes the error between the reference and predicted values. The minimization of the cost function is carried out to obtain the best switching state which is implemented to the inverter. Simulation analysis are performed in Matlab/Simulink with different operating conditions of the system to validate the effectiveness and feasibility of the proposed method.
Author: ,
Code: JST-UD2020-100 | Page: 7-10 of Vol. 18, No. 7, 2020 |
AbstractCurrently, renewable energy sources are being integrated into Vietnam's medium voltage system nationwide. According to Circular 39/2015 / TT-BCT of the Ministry of Industry and Trade, issued on November 18, 2015 on "Regulation of electric distribution system" referring to a number of technical regulations of the medium voltage network with respect to the frequency, voltage and protective relay systems [1]. However, this provision has not fully considered the changes and effects when connecting the distributed energy sources (DER) such as wind and solar to the medium voltage systems.The actual operation shows that the integration of renewable energy sources into medium voltage systems can cause several power quality problems such as overvoltage, adding more power loss, and affecting the protective relay, which were set up with the unidirectional power flow from the grid to the load [2-7]. This paper will focus on studying the impacts of the distributed energy sources on the protection of the power distribution systems.
Author:
Code: JST-UD2020-062 | Page: 11-17 of Vol. 18, No. 7, 2020 |
AbstractSliding mode control techniques have been developed and successfully applied to numerous kinds of robots. The disadvantage of the sliding mode control (SMC) is the chattering phenomenon occurring in the system. Accordingly, designers have to balance between the two objectives of the system namely are the transient time and the chattering level. This article adopts an exponential time-varying gain used in a SMC in order to better reduce the chattering degree and to decrease the transient time compared to a basic SMC using a constant gain. The SMC with the exponential time-varying gain will generate large control signals during the reaching stage, and maintain small control signals throughout the sliding stage to attenuate the chattering level. Theoretical analyses and numerical simulation results applied to the IRB 120 industrial robot reflect the advantage and the efficiency of using the exponential time-varying gain in the sliding mode controller.
Author: , Nguyễn Văn Điền,
Code: JST-UD2020-016 | Page: 18-23 of Vol. 18, No. 7, 2020 |
AbstractIn this paper, we build calculating model of Millimeterwave optical-wireless access system for next generation mobile communications using EDFA and coherent receiver for enhancing communication distance and the system sensitivity. We then calculate signal and total noise power at the end of optical fiber link and at mobile subscribers through wireless medium. After that, system performance showed by SNR, BER at the end of system is determined. They are investigated, compared, evaluated by Matlab in many different scenarios including BER performance vesus EDFA’s Gain, optical transmister power at central office (CO), optical oscillator power in coherent receiver, wireless frequencies, wireless length corresponding to two wireless cases of Line of Sight (LoS) and Non Line of Sight (NLoS). These results are considered good reference resource for designing, building and exploiting this Millimeterwave Optical-Wireless Access System in reality.
Author:
Code: JST-UD2020-099 | Page: 24-28 of Vol. 18, No. 7, 2020 |
AbstractAbstract: This study is to investigate some factors affecting the properties of the composites based on unsaturated polyester (UPE) and waste stone powders from Non Nuoc stone village, Danang city. The composite specimens are prepared by compression molding. The pressure of 40 Psi and pressing time of 2 hours are chosen. The mechanical tests including tensile, bending, compression and impact testing are carried out in order to investigate the influences of particle size and content of the waste stone powders on the properties of the stone powders/UPE composites. The fracture surfaces of the composites are also investigated by using scanning electron microscopy. The results show that the mechanical properties of the composites decrease while particle size and content of the waste stone powders increase, especially for the wet waste stone powders.
Author: , Hồ Trần Ngọc Anh, Phạm Văn Quang, ,
Code: JST-UD2020-114 | Page: 29-35 of Vol. 18, No. 7, 2020 |
AbstractAbstract - When adding HHO to gasoline, the combustion efficiency is improved, leading to an increase in maximum pressure and temperature, reducing CO and HC emissions but increasing NOx. When reducing the advance ignition angle, the concentration of CO increases slightly while the concentration of NOx sharply decreases. When adding 10% HHO to gasoline, the optimal advance ignition angle is reduced by 5CA compared to gasoline fueling mode. With the optimal advance ignition angle, when adding 10% HHO to gasoline the indicative engine work cycle increases by 7% and the concentration of NOx increases by 12% compared to gasoline operation. The experimental curves of variation CO, NOx according to engine speed has a lower slope than the corresponding simulation curves. The advance ignition angle of the gasoline-HHO engine can be adjusted to ensure a reasonable increase in power output but does not increase the level of pollutant emissions as compared to gasoline fueling mode.
Author: , Phan Huỳnh Nam
Code: JST-UD2020-096 | Page: 36-39 of Vol. 18, No. 7, 2020 |
AbstractEnergy plays an important role in socio-economic development as it enhances life quality of countries in the world; therefore, sustainable socio-economic development policies of each country are closely associated with national security, economic security and energy security. An issue of great concern is to find out alternative energy sources that can gradually replace fossil fuels which is being depleted day by day; one solution is biofuel energy used as a source of high-quality fuel, which can minimize environmental pollution. This article presents the research results aimed at enhancing the octane numeric value of the gasoline RON 90, which is charaterized by a low octane numeric value. With the additives Chimec Fa 162 and ethanol mixed in the gasoline RON 90, the octane numeric value increases dramatically but the other criteria still correspond to Viet Nam’s standards TCVN 6776:2013 for non-lead gasoline.
Author: , Phan Trần Đăng Khoa, Tôn Quang Hoàng Nguyên
Code: JST-UD2019-212 | Page: 40-46 of Vol. 18, No. 7, 2020 |
AbstractIn text classification field, most of previous studies only measured and evaluated the selected model upon one test set with a certain size, as well as did not clarify the training time of each model. This paper focuses on comparing and evaluating 3 text classification models: Support Vector Machine, Linear Regression using SGD, Naïve Bayes in terms of accuracy with different test sets, then clarifying the evaluation parameters with a test set of 900 input questions. Besides, the reseach compares the training time of each model at different training sets with varied training-sizes. The results have shown that Naïve Bayes has good accuracy and the training time is also significantly dominant when compared with the two others. Afterall, the author uses the above research results to propose a solution to build an admission chatbot through Facebook, provide promising empirical results and make it applicable to educational units in Vietnam.
Author:
Code: JST-UD2020-122 | Page: 47-50 of Vol. 18, No. 7, 2020 |
AbstractThis paper presents the method of using the blocking filters to prevent subsynchronous resonance problems in the electrical power system. The basis of the study stems from the requirement to prevent low frequency wave sources from the grid to the generator, to avoid resonance. The author has developped an algorithm to define filter parameters to eliminate frequencies that can cause resonant oscillations on turbine-generator shaft sections. The calculation results on the IEEE First Benchmark standard model have tested the efficiency of the filter method proposed in this paper. The computational analysis through the eigenvalue methods and the time domain simulation are also performed and compared.
Author:
Code: JST-UD2020-118 | Page: 51-55 of Vol. 18, No. 7, 2020 |
Abstract– In this research, n-butanol is used to recycle waste scooter lubricant by the extraction method. Monoethanolamine (MEA) is used as a flocculating agent that removes the contaminants from waste oil. The effect of temperature, solvent/ waste oil mass ratio and time of centrifugation on the recycling yield and the ash content are investigated. Optimization conditions of the extraction are obtained by experiments: temperature = 30oC, solvent/ waste oil mass ratio = 5/1 and time of centrifugation = 30 min. The recycling yield is 82,3%. The ash content of waste oil is 0,73% that has been decreased to 0,09% in recycled oil. The hydrocarbon characterization by FT-IR spectroscopic analysis illustrates that recycled oil is identified by aliphatic hydrocarbons, no containing aromatics and insaturate hydrocarbons, and can be used as lubricating base oil.
Author: Đỗ Minh Kỳ, Lưu Đức Bình
Code: JST-UD2019-148T | Page: 56-61 of Vol. 18, No. 7, 2020 |
AbstractNowadays, parametric design has been being widely applied in the field of manufacturing automatic mechanical components thanks to the CAD/CAM/CAE technology. The parameterization helps to flexibly provide a design drawing where one or more input parameters can be changed during the design process.This is of great significance for the production industry, since it reduces design time, quickly determines materials, and meets customers’ requirements. With that in mind, we have successfully built up a parametric model for the blanking and piercing die with the inputs being the overall specifications of the components based on the software Unigraphic NX 10.0. The research has been applied to the production at Chu Lai - Truong Hai Molds Manufacturing Company.
Author: ,
Code: JST-UD2020-048 | Page: 62-67 of Vol. 18, No. 7, 2020 |
AbstractIn this paper, a numerical scheme of the Discontinuous Galerkin (DG) method is proposed for the extended Navier-Stokes-Fourier equations in high-speed rarefied gas simulations. Two basic configurations in aerodynamics such as rarefied gas flows over the flat plate and circular cylinder in cross-flow, are adopted to verify the DG scheme aforementioned. Each configuration is simulated using the classical N-S-F and the extended N-S-F equations. All calculated results are compared with the Direct Simulation Monte-Carlo (DSMC) data, and show that those using the extended N-S-F equations are close to the DSMC data while those using the classical N-S-F equations are not, especially in the flat plate case.
Author: , Nguyễn Linh Giang, Lê Thanh Huyền
Code: JST-UD2020-111 | Page: 68-71 of Vol. 18, No. 7, 2020 |
AbstractTurbine Buld is a low water column turbine; the entire mass of machine is placed in the river bed which has a small capacity of less than 10MW. However, turbine designers and manufacturers always keep a secret about the turbine’s wing profile and operating characteristics. The manufacturers only provide basic dimensions for installation of the machine. Therefore, in order to have continuous operation with highly effectiveness of a hydroelectric and to reduce the dependence on experts from the manufacturers as well, the design of the turbine’s wing profile is very important in both engineering and economy. From the design drawings, manufacturing process is built for maintaining, reparing, and operating the hydroelectric plant. In this paper, basic steps for designing a Bulb turbine’s wing profile are presented. From the steps, a small model of turbine’s wing profile is designed and manufactured.
Author: Nguyễn Văn Đoài, , Trần Trọng Minh
Code: JST-UD2020-072 | Page: 72-78 of Vol. 18, No. 7, 2020 |
AbstractThis article introduces a solar battery system connected to a three-phase alternating current grid through the cascaded H-Bridge converter (CHB). The modularized structure of CHB converter helps to improve the efficiency and flexibility when using the PV system. To reduce valve switching losses and gain energy conversion efficiency, the paper proposes algorithm to control PI to CHB connecting grid with SVM modulation algorithm using the law of expanding any number of voltage levels and the ability to select the optimal valve switching state. This method has many advantages and is very suitable when applied to CHB to reduce losses during energy conversion. The algorithm can select the optimal valve switching state with any voltage level and does not need to list valve switching states compared to the previous SVM modulation methods. The simulation results of 3-level CHB system performed by matlab -simulink software have proved the feasibility of the proposed algorithm.
Author: Đồng Quốc Tranh, ,
Code: JST-UD2020-041 | Page: 79-83 of Vol. 18, No. 7, 2020 |
AbstractColorization is of great importance in restoring old gray pictures and making them more vivid. Thanks to the recent success of deep neural networks in various problems of computer vision, deep convolutional neural network has also been proposed for colorization and has brought about promising results. Yet previous works usually focus on some dataset and do not consider the influence of training data. This paper builds and evaluates many colorization models on various datasets according to criteria of image quality. The experimental results show interesting performance of residual networks in colorization. Moreover, an appropriate choice of training data may help to build an effective colorization model.